A novel and simple fluorescent sensor based on AgInZnS QDs for the detection of protamine and trypsin and imaging of cells.

• A novel fluorescence strategy based on MPA-AgInZnS QDs for sensitive and effective detection of protamine and trypsin. • This assay we investigated was simple, cost-effective, convenient and does not need any complicated pretreatment. • We successfully applied the AgInZnS QDs to intracellular imaging and lysosomes localization. In this study, a fluorescence strategy based on MPA-AgInZnS quantum dots (AIZS QDs) for the sensitive, effective detection of protamine and trypsin was developed. Protamine as a cationic peptide exhibited electrostatic interactions with AIZS QDs, leading to the aggregation of QDs and subsequent enhancement of the fluorescence intensity. The added trypsin catalyzed the hydrolysis of protamine and led to less formation of AIZS QDs/protamine complex, thereby decreasing the fluorescence intensity. Thus, a method for direct determination of protamine and indirect measurement of trypsin using protamine as a tool was developed. The protamine and trypsin concentrations were determined by the detection of the change in fluorescence intensity. Under the optimized conditions, the fluorescence intensity exhibited a good linear response to the protamine concentration, with a limit of detection (LOD) of 0.13 μg mL−1, and trypsin exhibited a linear relationship, with an LOD of 0.04 μg mL−1. The probe exhibited good biocompatibility and low cytotoxicity according to the MTT assay. Moreover, the application of this probe for intracellular imaging and lysosome localization demonstrates potential development in the biomedical and clinical fields. [ABSTRACT FROM AUTHOR]